1. Field of the Invention
The present invention relates to a multi-speed gearbox, and in particular, a six-speed gearbox for use with automatic transmissions.
2. Description of the Related Art
Multi-speed gearboxes in the form of automatic transmissions are known in a plurality of designs based primarily on a mechanical gearbox portion associated with an appropriate starting element. In particular, hydraulic torque converters or hydraulic couplings are used as starting elements in vehicle construction. The operating range of the hydraulic components is limited thereby primarily to the starting range. Gearbox designs are also possible with division of power in which, during the transmission of power the hydraulic component is used in the lower gears.
Automatic transmissions with starting elements in the form of hydraulic speed/torque converters are known, e.g., from Voith: xe2x80x9cHydrodynamics in Drive Technologyxe2x80x9d, Engineer Digest, Vereinigte Fachverlage Krausskopf-Verlag. Hydraulic torque converters can be divided into so-called converter gearboxes and differential converter gearboxes.
Converter gearboxes include all gearboxes in which a converter is connected to additional mechanical elements in order to bring about a change or expansion of the operating range of the gearbox. The converter can remain filled thereby during operation of the mechanical gear steps or can also be bridged filled or emptied. If the converter is placed into an outer power branch, it then no longer participates in the transmission of power in the mechanical gear steps and can remain filled.
Differential converter gearboxes are gearboxes with power branching in which the power flow is divided into a hydraulic branch and into a mechanical branch. A distinction can be made thereby between inner and outer power branching. A planetary gear set, as a rule a differential, can be combined, e.g., with a torque converter in such a manner that one element is connected to the pump impeller of the converter, the second element of the planetary gear set is connected to the drive shaft and the third element to the driven shaft. As the output speed increases, the hydraulically transmitted power component is reduced on account of the action of the differential whereas the mechanically transmitted component increases. This results in a higher degree of total efficiency for the gearbox than is the case for a purely hydraulic transmission of energy. Finally, the hydraulic converter is automatically bridged approximately at the operating point of its best efficiency and the power is transmitted purely mechanically.
A disadvantage of converter gearboxes is essentially the fact that the range which can be used for driving and which represents a certain translation ratio can only be achieved with relatively large converter units, which require a significant amount of space and are very expensive. All previously known solutions for planetary coupling gearboxes for bus gearboxes are characterized by translations which require a torque converter as an additional gear. These gearboxes can not be readily used because the first gear is always constituted by an individual planetary gear set for which the translation can not be increased further. A further disadvantage is the fact that the hydraulic converter is not self-regulating. It must therefore be adapted to each drive machine by changing the pump impeller and/or turbine and the differential.
The invention therefore has the basic problem of developing a gearbox unit of the initially cited type further in such a manner that the disadvantages cited are avoided. Specifically, a solution which is simple in design and can be realized with low expense for control technology is to be developed which makes it possible to realize a simple adaptation to various requirements, especially to drive engines, without significant additional expense.
According to the invention, in order to realize a multispeed gearbox the hydraulic converter is eliminated, such that the translation achievable with the converter is realized in a more cost-advantageous manner and with less complexity regarding the required construction space of an additional gear. This means that the mechanical gearbox portion is expanded by an additional gear. Another planetary gear set is preferably used to this end. The starting then takes place with a braking device for one of the gearbox elements of the planetary gear sets, preferably the ring gear, in which instance the braking device must be dimensioned as an inch brake. The dynamic viscosity of the oil forms the basis for this. The solution in accordance with the invention has the advantage of simpler control, since no centrifugal forces have to be compensated. Moreover, the braking device always cooperates during starting with the lowest engine speed, which speed can not be achieved with a converter. This results in a reduction of the fuel consumption.
There is a plurality of possibilities for the design of the gearbox. However, there is always a mechanical gearbox portion, which consists of a plurality of spur gear sets or planetary gear sets, as well as another mechanical gearbox set which is associated with an inch device, either in the form of an inch brake or an inch coupling.
The use of a so-called inch brake or also inch coupling offers yet another advantage over a hydraulic converter, namely, the possibility of remote control. An inch brake is preferably constructed with laminar design. The torque of an inch brake is controlled with the modulated oil pressure for the lamination pressure. As a result, the gearbox can be adapted to different engines and vehicle masses over a wide range exclusively by software.
The construction space is reduced in its axial length by using the inch device since large hydraulic converters can be eliminated. The mounting length could therefore be shortened for the entire gearbox or the gearbox could also be designed as a housing variant. The control for the shifting devices and the inch device can be placed above in mounting position. This means a simpler and more economical design than the previously known design for hydraulic converters with oil sump.
An inch device, preferably in the form of a multiple disk brake device, is used in the gearbox which device is also a shifting brake for the first gear and the reverse gear at the same time. The outer laminations are surrounded by an annular chamber. The latter is filled with oil during starting so that the laminations run fully in the oil. The oil exits at the inner diameter and flows from there into the oil sump. The oil inflow into the annular chamber is controlled with a magnet valve in the central control block of the gearbox. In the case of flooded laminations the torque is transmitted only by the shearing force of the oil. The laminations do not touch each other thereby. This can be calculated with the formula for the dynamic viscosity of the oil:
Vis=(Nxc3x97s/m2)
or also, unshortened,
Vis=Nxc3x97m/(m/s""m2)
in which
Vis=The viscosity of the oil at the instantaneous temperature
N (Newton)=The circumferential force on the laminations
m (m)=The oil slot between the laminations
m/s (m/s)=The average circumferential speed of the laminations
m2 (m2)=The entire lining surface moistened in the oil slot.
The product of Nxc3x97Rm (Nm) is then the torque transmitted by the brake. Rm indicates the average lamination radius.
During starting the greatest circumferential speed is present right at the beginning. This speed becomes smaller and smaller as the travel speed increases, so that the slot for constant torque must also become smaller and smaller until the lining contacts the counterlamination. Then, the outer oil is cut off and the laminations function just as in the other multiple disk brakes in the gearbox. The described property of the oil is also used in converter-inch couplings, in large control couplings, in wheel brakes in large construction machines, in VISCO couplings as differential lock in all-wheel vehicles, in oscillation dampers, etc.
The inch device can also be designed, e.g., as described in German Patent No. DE 195 14 276 A1. The disclosure of this publication, especially regarding the construction and method of operation of the device described in it, is included herewith to its full extent into the disclosed content of this application.
In particular, the multi-speed gearbox comprises at least one gearbox input shaft and one gearbox output shaft, a first mechanical gearbox portion, means for coupling the first mechanical gearbox portion to the gearbox input shaft and a starting element. According to the invention, another second mechanical gearbox portion is provided. This latter comprises at least one planetary gear set. A first gearbox element of the second mechanical gearbox portion is coupled to the first mechanical gearbox portion and to the gearbox output shaft. The starting element is designed as a braking device and associated with a further, second gearbox element of the second mechanical gearbox portion. Means for realizing the individual gear sets are associated with the first mechanical gearbox portion which can be actuated in such a manner that the translations can be determined in the first gear and in the reverse gear by the second mechanical gearbox portion.
The planetary gear set of the second mechanical gearbox portion comprises at least the following gearbox elements: A sun gear, a ring gear, a crosspiece and planetary gears. The first gearbox element is preferably formed by the sun gear and the second gearbox element by the crosspiece. A third gearbox element of the second mechanical gearbox portion is connected in a fixed-rotatable manner to a first gearbox partial element of the first mechanical gearbox portion.
The starting element is preferably designed as an inch brake. However, there is also the possibility of designing it as an inch coupling. It is preferable to use starting elements with a laminar design.
The means for realizing the gear steps are designed in the form of coupling devices and/or braking devices, preferably with a laminar design.
A plurality of possibilities are available for the design of the first mechanical gearbox portion. In principle, any variant is conceivable which makes available the possibility of a series coupling of the second mechanical gearbox portion for the starting gear and reverse gear. For example, a variant with three planetary gear sets is conceivablexe2x80x94a first planetary gear set, a second planetary gear set and a third planetary gear set. Each planetary gear set comprises as gearbox elements at least one sun gear, one ring gear, a crosspiece and planetary gears. A first gearbox element of the first planetary gear set is connected in a fixed-rotatable manner to the gearbox input shaft. A second gearbox element of the third planetary gear set is connected in a fixed-rotatable manner to the gearbox output shaft. The first gearbox element of the first planetary gear set of the first mechanical gearbox portion is formed by the sun gear. The second gearbox element of the third planetary gear set of the first mechanical gearbox portion is preferably formed by the crosspiece.
The third gearbox element of the second mechanical gearbox portion is connected in a fixed-rotatable manner to the third gearbox element, designed as first gearbox partial element, of the third planetary gear set of the first mechanical gearbox portion. The third gearbox element of the third planetary gear set of the first mechanical gearbox portion is formed thereby by its ring gear. The third gearbox element of the second mechanical gearbox portion is preferably also formed by its ring gear.
The means for realizing the individual gear steps comprise at least two coupling elementsxe2x80x94a first coupling element and a second coupling element as well as at least three brake devicesxe2x80x94a first brake device, a second brake device and a third brake device. The first gearbox elements of the second and of the third planetary gear set can be coupled at least indirectly to the gearbox input shaft by the first coupling element. A further, second gearbox element of the second planetary gear set and a third gearbox element of the third planetary gear set can be coupled to the gearbox input shaft by the second coupling element. A brake device is associated with a further, third gearbox element of the first, the second and the third planetary gear set of the first mechanical gearbox portion. The first gearbox elements of the second and of the third planetary gear set of the first mechanical gearbox portion are preferably formed by the sun gear. The second gearbox element of the second planetary gear set of the first mechanical gearbox portion is formed by the crosspiece, and the third gearbox elements of the individual planetary gear sets of the first mechanical gearbox portion are formed by the ring gears.
The gearbox arrangement of the invention can be combined with further elements, e.g., with at least one power take-off for driving other vehicle components, e.g., a ventilator [cooling fan] or right-angle gear drives. Furthermore, the use of a hydraulic retarder in the entire gearbox is also conceivable.